Migrating a PostgreSQL Database to SQL Anywhere 12 - Sybase

spaces in the previous example with zeros and add the UNSIGNED attribute to the column. For example, ‘1’ is
returned as ‘0001’. The merge of display format and data values in the type definition is not supported by SQL
Anywhere. The CAST and CONVERT functions, along with the various string manipulation functions are
available to format data values when they are retrieved from the database.
The following data types differ from SQL Anywhere more substantially than by syntax:
MEDIUMINT: These are 3-byte integer values. They can easily be simulated using an INTEGER (4 bytes) or
SMALLINT (2 bytes) in SQL Anywhere, depending on the expected range of values for the column.
YEAR: Year is a 2 or 4 digit value. The SQL Anywhere DATE data type can be used to hold year values, but uses
slightly more storage space. Date arithmetic and conversion can be performed using the SQL Anywhere builtin
functions listed under “Date and Time Functions” in the “SQL Functions” chapter of the “SQL Anywhere
Server - SQL Reference” manual.
The following data types do not match exactly, and will require some work to migrate to SQL Anywhere:
NCHAR/NVARCHAR: As of PostgreSQL 5, an NCHAR value is stored in PostgreSQL using the UTF8 character set.
SQL Anywhere supports a variety of character sets, including UTF8. With a database created using the proper
collation, the use of a special data type to store international values is not required, though SQL Anywhere does
support the NCHAR data type. To learn more about the latest international character set support in SQL
Anywhere, see the chapter “International Language and Character Sets” in the “SQL Anywhere Server -
Database Administration” manual.
ENUM: An ENUM value is a string object whose value must be chosen from a list of supplied values enumerated
in the column definition when a table is created. The enumerated values can also be inserted or retrieved by
their index position in the ENUM definition. The index value 0 is reserved for the empty string. The ENUM
data type is represented in SQL Anywhere by a TINYINT column. There are a few options to accomplish the
same behavior as the PostgreSQL ENUM, but changes to the client application will almost certainly be required.
Some options are:
• Altering the client side application to remove the need for ENUM values
• Translating the ENUM values on the client side
• Adding some logic to the server side to attempt to mimic the PostgreSQL behavior of ENUM values
by using stored procedures, triggers, computed columns, view, and/or a mapping table for the
ENUM types
For example, a view could be created on the table containing the ENUM fields to allow for the return of the
values as a string, while a regular SELECT could be used to return them as a number. Here is an example of a
view that could be used:
CREATE TABLE enumtbl (pkey INTEGER NOT NULL PRIMARY KEY, enumval TINYINT);
CREATE VIEW v_enumtable AS
SELECT pkey
CASE WHEN 0 then ‘’
WHEN 1 then ‘val1’
WHEN 2 then ‘val2’
WHEN 3 then ‘val3’
ELSE NULL
END
FROM enumtbl;
Then, a query may look something like this:
SELECT pkey, enumval FROM v_enumtable;
Alternatively, a mapping table could be created for the ENUM vales and whenever you retrieve data from
enumtbl, a join can be made to the mapping table containing the ENUM strings.
Migrating a PostgreSQL Database to SQL Anywhere 12
December 2011
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